Process for making a liquid absorbing thermoplastic material

ABSTRACT

The present invention relates to an improved process for making liquid absorbing thermoplastic materials comprising a thermoplastic polymeric composition and an absorbent material in particle form dispersed in the thermoplastic polymeric composition. Such liquid absorbing thermoplastic material can be utilised in the absorbent cores of disposable absorbent articles, such as sanitary napkins, panty liners, interlabial devices, tampons, disposable diapers, incontinence pads, wound dressings, nursing pads and the like for completely or partially substituting said absorbent cores.

FIELD OF THE INVENTION

The present invention relates to a process for making a liquid absorbingthermoplastic material, comprising a thermoplastic polymeric compositionhaving absorbent particles dispersed therein. Such liquid absorbingthermoplastic materials can be utilized in a number of end uses whereliquid absorption is desired, for example in the absorbent core ofdisposable absorbent articles, such as sanitary napkins, panty liners,interlabial devices, tampons, disposable diapers, incontinence pads,wound dressings, nursing pads and the like for completely or partiallysubstituting said absorbent core.

BACKGROUND OF THE INVENTION

In general the absorption and retention of aqueous liquids, particularlybody fluids such as urine, menses, etc., are accomplished by use ofabsorbent articles containing absorbent materials. Such articles includesanitary napkins, panty liners, interlabial devices, tampons, disposablediapers, incontinence pads, wound dressings, nursing pads, and the like.Generally, the most used absorbent materials are cellulose materials(e.g., defiberised wood pulp) and superabsorbent materials. Inparticular, when referring to disposable diapers or sanitary napkins andthe like presently available in the market, the cellulose materials arein the form of bat or sheet, typically further containing particulateabsorbent materials, usually referred to in the art as superabsorbentsor hydrogelling materials, which allow to manufacture thin but veryabsorbent core structures. A primary need in incorporatingsuperabsorbent material in particle form within an absorbent structureis its stabilization, in order to counteract the tendency of powderedmaterial to bunch up or agglomerate, hence providing an unevenabsorptive capacity in the absorbent structure, or also to dust off thestructure itself. Known approaches are for example to adhesively fix theparticles into a fibrous structure, or to disperse the powderedsuperabsorbent material in a fibrous matrix, e.g., cellulose pulp, andfix it in place mechanically, e.g., by calendaring or embossing. Analternative approach is to blend a superabsorbent particulate materialinto a thermoplastic matrix, e.g., a thermoplastic composition. Thesuperabsorbent containing thermoplastic composition can be typicallyextruded or coated in any desired position and pattern onto a suitablesubstrate, to be then incorporated into an absorbent article, thusentirely providing the absorbent material in the article, oralternatively integrating a more traditional fibrous absorbentstructure, with no risk of dust off of the particulate material, ordisplacement within the absorbent structure of the article. For example,EP 1013291 and WO 98/27559 describe a hot melt adhesive containing asuperabsorbent polymer. WO 99/57201 illustrates compositions comprisinga thermoplastic component and a superabsorbent polymer, saidcompositions in form of a film layer or applied to a disposableabsorbent article with various hot melt adhesive application techniques.Applications WO 03/049777 and WO 04/028427 respectively describethermoplastic compositions comprising a matrix of a thermoplasticpolymeric composition and superabsorbent particles dispersed therein,which have a particularly effective fluid acquisition and handlingcapacity, and absorbent articles comprising superabsorbent containingthermoplastic compositions arranged in a pattern of unattached spacedapart zones.

The technology of composite thermoplastic materials comprising a matrixof a thermoplastic composition and particles of superabsorbent materialdispersed therein has provided a solution to the problem of powderedsuperabsorbent material “instability” within absorbent structures inabsorbent articles, preventing particle displacement as, e.g., dust-off,agglomeration, or bunching up, and safeguarding the end users ofabsorbent articles virtually from any undesired contact with thesuperabsorbent particles upon normal use. This technology has alsoallowed the use in absorbent articles of superabsorbent materials in amuch smaller particle size than previously adopted for traditionallymanufactured fibrous absorbent structures with superabsorbent materials.Such reduced average particle size, generally in the range below about150μ, about 10μ to about 40μ, as disclosed for example in WO 04/028427,is advantageous not only in terms of better liquid handling andabsorption capacity of the corresponding thermoplastic absorbentcompositions, due to the increased surface/volume ratio provided bysmaller particles, but also in an easier processability of thethermoplastic material, which may have lower viscosities at the processconditions, typically a hot melt extrusion onto a substrate.

However, powdered superabsorbent materials also pose health risks tothose involved in the manufacturing process, particularly when they aremanufactured in very small particle sizes as mentioned above. The finelypowdered superabsorbent material can become airborne and can be inhaledby workers. Once inhaled, the superabsorbent material absorbs liquidwithin the respiratory passages swelling to many time its original size.This can result in blocked air passages and potentially traumatic healthcomplications.

According to the known technique, liquid absorbing thermoplasticmaterials comprising a matrix of a thermoplastic composition withsuperabsorbent particles dispersed therein are manufactured by providinga) the superabsorbent material in the desired, and possibly very small,particle size, usually achieved by grinding coarser particles, b) thecomponents of the thermoplastic composition, and c) by uniformly mixingthem all upon sufficient heating, in order to melt the components of thethermoplastic composition. Hence the superabsorbent material has to betypically handled in a very small particle size, namely manufactured,shipped and then processed in the production line of the liquidabsorbing thermoplastic composition. Shipping of superabsorbentmaterials in very low particle size is also subjected to severelimitations in many countries, based on health and environmentalgrounds. On the other hand provision of superabsorbent material in thedesired very low particle size starting from coarser and environmentallyless demanding particles directly in the same line of production of thefinal liquid absorbing thermoplastic material is not always convenient,since it necessarily implies addition of a grinding station to theproduction line, which does not allow much flexibility in themanufacturing process of the liquid absorbing thermoplastic material,and increases complexity. It also implies in any case handling of finesuperabsorbent particles at a certain stage of the process.

Hence there is the need for a process for making a liquid absorbingthermoplastic material comprising a matrix of a thermoplasticcomposition and absorbent particles, typically particles ofsuperabsorbent material, dispersed therein which is more flexible andallows the use of particles in the desired low particle size, withoutthe limitations and drawbacks created by the handling of such very fineparticles.

It would, therefore, be desirable to provide an improved process formaking a liquid absorbent thermoplastic material, which allows a simplerand safer handling of the absorbent materials in very low particlesizes. It would also be desirable to provide a process for making atypically liquid absorbing thermoplastic material wherein particles ofsuperabsorbent material can be manufactured in any desired particlesize, and then possibly further handled, e.g., stocked or shipped,before provision to the liquid absorbing thermoplastic materialproduction line.

SUMMARY OF THE INVENTION

The present invention provides a process for making a liquid absorbingthermoplastic material comprising a matrix of a thermoplastic polymericcomposition and particles of absorbent material dispersed in the matrix,wherein the thermoplastic polymeric composition comprises at least twocomponents. The process comprises the following steps:

providing the particles of absorbent material, mixing the particles ofabsorbent material with a first component in the liquid state of the atleast two components forming a pre-mix, mixing the pre-mix with a secondcomponent of the thermoplastic polymeric composition in the moltenstate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a production line for the manufactureof a liquid absorbing thermoplastic material according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

By “liquid” as herein used is meant water based fluids or liquids suchas urine, menses, serum, blood, sweat, mucous as well as other aqueoussolutions generally defined as body fluids, but it is not intended toexclude other water based fluids.

By “room temperature” as herein used is conventionally meant atemperature of 25° C., as known in the art.

For purposes of the present invention, viscosity has to be meant as meltviscosity at a certain temperature, which is determined with anysuitable apparatus as known in the art. Particularly, viscosity can bedetermined with the procedure and apparatus described on page 22 of thealready cited PCT application WO 99/57201, to which reference is made,in the paragraph headed “Melt Viscosity”, possibly with the necessaryadjustments, e.g., spindle selection, for measuring viscosities below 10centipoises.

For purposes of the present invention, particle size is defined as thedimension of a particle which is determined by means of any suitablemethod known in the art for particle sizes comprised in the rangeaccording to the present invention. Particularly indicated are laserlight scattering analysis or laser diffraction analysis. The averageparticle size of a given sample is defined as the particle sizecorresponding to a cumulative distribution of 50% of the particles ofthe sample. In other words, the average particle size of a given sampleof absorbent material particles is defined as the particle size whichdivides the sample in half on a mass basis, i.e., half of the sample byweight will have a particle size greater than the average particle sizeand half of the sample by weight will have a particle size less than theparticle size.

The process of the present invention will be herein described withreference to the production of a liquid absorbing thermoplastic materialwherein the particulate absorbent material is in fact a water-insolublewater-swellable material in particle form, but of course the presentinvention refers to any liquid absorbing thermoplastic materialcomprising a different absorbent particulate material.

FIG. 1 shows a production line for the manufacture of a liquid absorbingthermoplastic material comprising a matrix of a thermoplastic polymericcomposition and particles of water-insoluble water-swellable absorbentmaterial dispersed therein. The matrix of thermoplastic polymericcomposition comprises at least two components.

The particles of water-insoluble water-swellable absorbent material 10are provided from a supply means, for example a container 15, and thefirst component 20 in the liquid state of the thermoplastic polymericcomposition is provided from a respective suitable supply means,typically a tank or vessel 25. The particles 10 and the first component20 in the liquid state are conveyed in the desired amounts andproportions by suitable means, e.g., the tubing 27, to a mixing device30, where they are uniformly mixed to form a pre-mix 35. Preferably, thefirst component 20 of the thermoplastic polymeric composition is liquidat room temperature (25° C.), such that it can be directly provided inthe liquid state from the tank or vessel 25 to the mixing device 30. Thepre-mix 35 is such a case is typically a slurry which is more or lessviscous or pasty at room temperature. Alternatively, the first component20 can be solid or semi-solid at room temperature (25° C.), and broughtto the liquid state by suitably heating it with known heating meansbefore or upon providing it to the mixing device 35. In one embodiment,the first component 20 is selected such that at room temperature it isliquid, and also has a viscosity below about 30,000 centipoise, belowabout 10,000 centipoise, below about 5,000 centipoise, between about 1and about 4,000 centipoise, or between about 10 and about 3,000centipoise. Low viscosity at room temperature of the liquid firstcomponent 20 provides the advantage of an easier and more effectivemixing with the particles of water-insoluble water-swellable absorbentmaterial 10 in order to form the pre-mix 35 in the mixing device 30.Less energy is in fact required for the mixing step, as well as forhandling and conveying the first component 20, typically from the tankor vessel 25 to the mixing device 35, and of the pre-mix 35 as wellfurther of the mixing device 35. A uniform mixing of the particles ofwater-insoluble water-swellable absorbent material 10 and of the firstcomponent 20 may be more easily and effectively achieved because of therelatively low viscosity of the first component 20 at room temperature.

If desired, a controlled heating can be also provided to a firstcomponent which is liquid already at room temperature, in order tofurther reduce its viscosity and preferably bring it in the desiredrange for the mixing step where the pre-mix is formed. Such viscositiescan be also provided by suitably heating and melting a first componentin said mixing step in the less preferred embodiment when the firstcomponent is solid at room temperature.

The pre-mix 35 is then further processed in order to form the finalliquid absorbing thermoplastic material. This further process can beperformed directly in the same production line, right after theformation of the pre-mix 35, or alternatively the pre-mix can betemporarily stored, in order to be subsequently fed to the productionline of the liquid absorbing thermoplastic material, in the samefacility, or alternatively shipped to another facility for this finalproduction step. In any case, the handling, storing and/or shipping ofthe pre-mix 35 constituted by the first component 20 preferably liquidat room temperature, comprising the particles of water-insolublewater-swellable absorbent material 10 dispersed therein, is greatlysimplified with respect to the handling, storing and/or shipping of theparticles of water-insoluble water-swellable absorbent material alone.

The pre-mix 35 may be conveyed by a suitable means to a melting andmixing station 40 where a second component 45 meant to constitute thethermoplastic polymeric composition is also fed in the desired amountfrom a container 50. Alternatively, multiple other components can bealso provided in the desired amounts, for example from respectivecontainers, to the melting and mixing station 40, where they aresuitably heated and melted, with known means and according to the knowntechnology of thermoplastic polymeric composition production, andcompounded with the pre-mix 35 containing the first component 20 of thethermoplastic polymeric composition, with the particles ofwater-insoluble water-swellable absorbent material 10 already dispersedtherein. The final liquid absorbing thermoplastic material 55 comprisingthe matrix of the thermoplastic polymeric composition with the particlesof water-insoluble water-swellable absorbent material 10 dispersedtherein is then formed, and can be provided for further uses andproduction steps according to known techniques, for example directlyapplied in the molten state onto a suitable substrate, or solidified andstored in suitable forms, e.g., pellets, for further uses. The finalliquid absorbing thermoplastic material 55 is typically solid at roomtemperature.

The pre-mixing of the particles of water-insoluble water-swellableabsorbent material 10 with a first component 20 in liquid form of thethermoplastic polymeric composition in the process of the presentinvention, solves the problems generally implied by the handling ofmaterials in form of fine and very fine particles, particularly theenvironmental and health problems related to the handling of particlesof water-insoluble water-swellable absorbent material. This in turnallows the use of particles having a very low average size, which aregenerally advantageous in that they allow an easier processability ofthe thermoplastic material comprising the particulate material. As it isknown, addition of solid particles into a matrix of a thermoplasticpolymeric composition increases the overall viscosity of thethermoplastic material in the molten state at given conditions, whencompared with the viscosity of the same matrix without particles, at thesame conditions. Selection of particles having a preferred low or verylow average size reduces this effect, providing a less viscousthermoplastic material in the molten state at the same conditions, hencefacilitating the handling and processing of the thermoplastic material,for example when applying it onto a substrate by means of knownextrusion or hot melt coating techniques. Smaller particles also providean increased surface to volume ratio compared to larger particles, hencegenerally enhancing their functionality. Particularly, water-insolublewater-swellable absorbent material in particle form provides enhancedabsorption capacity and absorption rate when in very small particlesize, owing to the increased surface to volume ratio. It is desirablethat the absorbent particulate material comprised in the matrix ofthermoplastic polymeric composition to form the liquid absorbing,thermoplastic material made with the process of the present inventionhas an average particle size below about 150μ, below about 40μ, betweenabout 1μ and about 30μ, or where the average particle size is betweenabout 10μ and about 20μ.

Particulate absorbent material of the very low particle size can behandled and also shipped with no concern of health and environmentalrisks according to the process of the present invention, since it can beprovided, e.g., by grinding coarser particles to the desired particlesize, or directly synthesized in the desired particle size, and thenmixed with the first component in the liquid state of the matrix ofthermoplastic polymeric composition to form the pre-mix, and thenactually handled and/or shipped as a semi-liquid slurry, with noexposure of dust or fine particles. The pre-mix moreover constitutes aningredient of the final liquid absorbing thermoplastic material, whichcan be prepared by simply compounding the pre-mix with the othercomponent or components of the thermoplastic matrix by suitably meltingand mixing according to known technique, with no need of separating theparticulate material from the first component in the liquid state beforethe final compounding step, as it would happen with liquid carriers forparticulate materials which are known in the art.

The liquid absorbing thermoplastic material prepared according to oneprocess of the present invention comprises a matrix of a thermoplasticpolymeric composition with particles of a water-insolublewater-swellable absorbent material dispersed therein.

In general, particulate absorbent materials for the manufacturing of aliquid absorbing thermoplastic material according to the process of thepresent invention can be selected among known particulatewater-insoluble, water-swellable absorbent materials, as alreadymentioned, or also among particulate liquid gelling materials.

Particulate water-insoluble water-swellable absorbent materials compriseknown, typically crosslinked, absorbent materials which are usuallyreferred to as “hydrogels”, “super absorbents”, “absorbent gellingmaterials” (AGM). Such materials, upon contact with aqueous fluids,especially aqueous body fluids, imbibe such fluids and thus formhydrogels by swelling of their own three-dimensional network provided bycrosslinking. These absorbent materials are typically capable ofabsorbing large quantities of aqueous body fluids, and are furthercapable of retaining such absorbed fluids under moderate pressures.These absorbent materials are typically in the form of discrete, nonfibrous particles, even if super absorbents in fibre form are known.

Any commercially available super absorbent material in particle form issuitable for the liquid absorbing thermoplastic material made with theprocess of the present invention. Suitable super absorbent materials foruse herein will most often comprise a substantially water-insoluble,slightly crosslinked, partially or fully neutralized, polymeric gellingmaterial. This material forms a hydrogel upon contact with water. Suchpolymer materials can be prepared from polymerizable, unsaturated,acid-containing monomers. Suitable materials are polyacrylate basedsuperabsorbent polymers in particle form.

Particulate absorbent materials to be included in the liquid absorbingthermoplastic material made with the process of the present inventioncan also comprise particulate liquid gelling materials, which arematerials, typically not crosslinked, which upon contact with liquidform a gel creating a three-dimensional network by interacting with themolecules present in the liquid, such as typically proteins, lipids, andso on in body fluids. Liquid gelling materials can be selected forexample among polysaccharides, starches, modified cellulose. Suitableliquid gelling materials according to the present invention are cationicpolysaccharides, including, but not limited to, chitosan and itsderivatives, where the creation of a three-dimensional network uponcontact with liquid, and hence gelification, is achieved by formation ofelectrostatic bonds between the positively charged cationic groups ofthe cationic polysaccharide and the negatively charged electrolytescontained in the fluid.

Suitable chitosan materials to be used herein include substantiallywater-soluble chitosan. Suitable chitosan materials for use herein maygenerally have a wide range of average molecular weights, typicallyranging from about 1,000 to about 10,000,000, about 2,000 to about1,000,000. Suitable chitosan materials for use herein are chitosansalts, particularly water-soluble chitosan salts. A variety of acids canbe used for forming chitosan salts, namely inorganic and organic acids.Chitosan salts formed by the reaction of chitosan with an amino acid arealso suitable for use herein.

Examples of chitosan salts formed with an inorganic acid include, butare not limited to, chitosan hydrochloride, chitosan hydrobromide,chitosan phosphate, chitosan sulphonate, chitosan chlorosulphonate,chitosan chloroacetate and mixtures thereof. Examples of chitosan saltsformed with an organic acid include, but are not limited to, chitosanformate, chitosan acetate, chitosan lactate, chitosan glycolate,chitosan malonate, chitosan epoxysuccinate, chitosan benzoate, chitosanadipate, chitosan citrate, chitosan salicylate, chitosan propionate,chitosan nitrilotriacetate, chitosan itaconate, chitosan hydroxyacetate,chitosan butyrate, chitosan isobutyrate, chitosan acrylate and mixturesthereof. It is also suitable to form a chitosan salt using a mixture ofacids including, for example, both inorganic and organic acids. Onesuitable chitosan salt for use herein is chitosan lactate.

According to the process of the present invention, the pre-mix maycomprise from about 40% to about 80%, from about 50% to about 70%, byweight of the pre-mix, of particles of absorbent material, and fromabout 20% to about 60%, from about 30% to about 50%, by weight of saidpre-mix, of the first component of said thermoplastic polymericcomposition. The final liquid absorbing thermoplastic material made withthe process of the present invention may comprise from about 10% toabout 90%, from about 15% to about 70%, from about 20% to about 60%, byweight of the liquid absorbing thermoplastic material, of particles ofabsorbent material.

The average particle size of the liquid absorbent particulate material,e.g., of a water-insoluble water-swellable absorbent material, usedherein is preferably low, typically below about 150μ, below about 40μ,between about 1μ and about 30μ. An average particle size between about10μ and about 20μ may be desired for water-insoluble water-swellableabsorbent materials.

Small particle sizes may be desired as this may result in improvedperformance and processability for the liquid absorbing thermoplasticcomposition prepared according to the process of the present invention.In an embodiment of the present invention, particulate absorbentmaterials comprised in the liquid absorbing thermoplastic material madewith the process of the present invention can be synthesized accordingto known processes such as they have the desired low average particlesize. Examples are superabsorbent materials having substantially aspherical shape commercially available from Sumitomo Seika in differentaverage particle sizes under the trade name Aquakeep® 10SH-NF. However,the desired low average particle size may be achieved by suitablygrinding a coarser material. Ground particulate absorbent materials, forexample, ground superabsorbent materials, are often cheaper compared tomaterials directly prepared in the selected average particle size, andare commonly used in absorbent articles. Manufacturing, such as forexample by grinding, and generally handling particulate materials in lowand very low average particle sizes, particularly superabsorbentmaterials, pose as already explained health and environmental risks,especially when said materials are manufactured in the low and extremelylow average particle sizes preferred for the liquid absorbingthermoplastic material made with the process of the present invention.According to one embodiment of the present invention, the process formaking the liquid absorbing thermoplastic material described so farcomprises the further step of grinding the particles of the absorbentmaterial directly into the pre-mix with known means to the selected lowaverage particle size, such that the particulate absorbent material canbe provided to the pre-mixing step in a relatively large averageparticle size which is easily available in the market and alsoprocessed/handled without special care.

Alternatively, the grinding step can be performed onto to particulateabsorbent material already dispersed and compounded into thethermoplastic polymeric composition, typically in the molten state, as alast step in order to obtain the particulate absorbent material in theselected low average particle size in the liquid absorbing thermoplasticmaterial.

Although the above process, namely in its alternative execution,includes a grinding station in the production line of the liquidabsorbing thermoplastic material, it has the advantage that theparticulate absorbent material in low and very low average particle sizeis never present as such, i.e., as a free, dry powder, in anymanufacturing step either of the pre-mix or of the liquid absorbingthermoplastic material, thus completely avoiding the health andenvironmental issues related to the handling of particulate absorbentmaterial in very fine average particle size.

It is desirable that the absorbent material in particle form, typicallythe water-insoluble water-swellable absorbent material, is present inthe liquid absorbing thermoplastic material made with the process of thepresent invention in an amount from about 10% to about 90%, from about15% to about 70% and from about 20% to about 60% by weight of the totalliquid absorbing thermoplastic material.

The liquid absorbing thermoplastic material made according to theprocess of the present invention further comprises as an essentialelement a matrix of a polymeric thermoplastic composition typically at alevel from about 10% to about 90%, from about 30% to about 85%, fromabout 40% to about 80% by weight of the liquid absorbing thermoplasticmaterial.

Any thermoplastic polymeric composition known to the skilled person andsuitable to form the matrix in the liquid absorbing thermoplasticmaterial made by the process of the present invention can be usedherein, provided it comprises at least two components, with a firstcomponent intended to be mixed in the liquid state with the absorbentparticulate material to form the pre-mix. The first component is inertto the particulate material, that is to say it is substantially nonreactive with the absorbent material in particle form. Preferably, theabsorbent material in particle form is also substantially insoluble inthe first component, such that the absorbent material keeps itsparticulate state in the pre-mix with the first component and in thefinal liquid absorbing thermoplastic material. In embodiments where thefirst component of the thermoplastic polymeric composition is liquid atroom temperature, it may have at room temperature a viscosity belowabout 30,000 centipoise, below about 10,000 centipoise, below about5,000 centipoise, between about 1 and about 4,000 centipoise, betweenabout 10 and about 3,000 centipoise. The thermoplastic polymericcompositions for use herein typically comprise thermoplastic polymers asan essential element. Thermoplastic polymer or mixtures of polymers arepresent in amounts typically ranging from about 5% to about 99%, about10% to about 90%, from about 30% to about 70%, or from about 40% toabout 60% with respect to the total weight of the thermoplasticpolymeric composition forming the matrix.

The matrix of thermoplastic polymeric composition can be also formulatedas a hot melt adhesive, as it is known in the art, hence typicallycomprising, e.g., a thermoplastic polymer, a plasticiser and a tackifierresin. Of course the hot melt adhesive constituting the matrix mustcomprise at least a first component to be mixed in the liquid state withthe particulate material, preferably a first component which is liquidat room temperature.

Liquid absorbing thermoplastic materials comprising particles ofwater-insoluble water-swellable material are already known in the art,and can be prepared according to the process of the present invention.For example, materials described in patent applications WO 98/27559 andWO 99/57201 can be prepared with the process of the present invention.

The thermoplastic polymeric composition may comprise one or morethermoplastic polymers and a suitable compatible plasticiser, whereinthe plasticiser is the first component which is mixed in the liquidstate with the absorbent particulate material, preferably with particlesof water-insoluble water-swellable material, in order to form thepre-mix. The pre-mix is subsequently compounded with the otherthermoplastic polymer or polymers comprised in the thermoplasticpolymeric composition.

The suitable compatible plasticiser may be liquid at room temperatureand may have the viscosity at room temperature as specified above.

According to one embodiment of the present invention, the thermoplasticpolymer can be selected from the group consisting of polyurethanes,poly-ether-amides block copolymers, polyethylene-acrylic acid andpolyethylene-methacrylic acid copolymers, polyethylene oxide and itscopolymers, ethylene acrylic esters and ethylene methacrylic esterscopolymers, poly lactide and copolymers, polyamides, polyesters andcopolyesters, polyester block copolymers, sulfonated polyesters,poly-ether-ester block copolymers, poly-ether-ester-amide blockcopolymers, polyacrylates, polyacrylic acids and derivatives, ionomers,polyethylene-vinyl acetate with a vinyl acetate content of at least 28%by weight, polyvinyl alcohol and its copolymers, polyvinyl ethers andtheir copolymers, poly-2-ethyl-oxazoline and derivatives, polyvinylpyrrolidone and its copolymers, thermoplastic cellulose derivatives,poly-caprolactone and copolymers, poly glycolide, polyglycolic acid andcopolymers, polylactic acid and copolymers, polyureas, and the suitablecompatible plasticiser can be selected from the group consisting ofcitric acid esters, tartaric acid esters, glycerol and its esters,sucrose esters, adipates, sebacates, sorbitol, epoxidized vegetal oils,polymerised vegetal oils, polyols, phthalates, liquid polyesters,glycolates, glycols and polyglycols and their derivatives, sorbitanesters, phosphates, monocarboxylic fatty acids (C₈-C₂₂) and theirderivatives, mineral oils, high boiling point alcohols, glycerin, glycolethers, which are preferably liquid at room temperature (or 25° C.).

Suitable thermoplastic polymers are selected from thermoplasticpoly-ether-amide block copolymers (e.g., Pebax™), thermoplasticpoly-ether-ester-amide block copolymers, thermoplastic polyester blockcopolymers (e.g., Hytrel™), thermoplastic polyurethanes (e.g., Estane™),and polyethylene-vinyl acetate with a vinyl acetate content of at least28% by weight.

Suitable plasticisers include mineral oils, high boiling point alcohols,glycerin, and glycol ethers. Other suitable plasticisers includepolyethylene glycols, polypropylene glycols, and derivatives thereof,suitably selected such as they are liquid and have the preferredviscosity at room temperature.

One suitable liquid absorbing thermoplastic composition comprisingparticles of superabsorbent material, which can be made with the processof the present invention, is described in patent application WO03/49777. This application discloses thermoplastic polymeric basematerials for use in the liquid absorbent thermoplastic compositions tobe applied in the absorbent articles of the present invention, whichhave a water absorption capacity at least greater than about 30%,greater than about 40%, greater than about 60% and greater than about90%, when measured according to the Water Absorption Test describedherein in accordance with ASTM D 570-81, on a film 200 μm thick. Theintrinsic absorbency of the polymeric base material/matrix allows for amore effective diffusion of the body fluid within the matrix and,consequently, for a better spreading of the body fluid which can reach agreater number of absorbent material particles which in turn give riseto a better utilization of the absorbent material.

Suitable liquid absorbent thermoplastic compositions described in WO03/49777 are those showing good integrity in wet state and hence havinga tensile strength in wet state which is at least about 20%, at leastabout 40%, or at least about 60% of the tensile strength of thecomposition in dry state. The tensile strengths are evaluated accordingto the Tensile Strength Test described herein. It should be appreciatedthat by selecting a thermoplastic base material, in the liquid absorbentthermoplastic composition herein having a higher value of waterabsorption, the absorbent composition will have better liquidabsorption/handling characteristics, while not compromising on tensilestrength in wet state. Indeed such absorbent composition will remainsubstantially intact and have sufficient tensile strength for itsintended use, also upon liquid absorption.

EXAMPLE ACCORDING TO THE INVENTION

A liquid absorbing thermoplastic material is prepared according to thefollowing process. A particulate superabsorbent material wherein 100% ofthe particles has an average particle size below 25μ, as measured, e.g.,by Laser Light Scattering Method, is prepared by suitably grinding thematerial available from Nippon Shokubai Co. Ltd. under the trade nameAqualic CA Type L74 to the desired particle size, e.g., in a Fluid BedCounter Mill AFG from Hosokawa Alpine. A pre-mix is formed by adding anduniformly dispersing at room temperature the particulate superabsorbentmaterial into a polyethylene glycol (M.W. 400) available from Dow EuropeGmbH under the trade name Carbowax™ PEG 400E. The pre-mix has thefollowing composition in percent by weight: 40% PEG 400 60% Aqualic L74

The liquid absorbing thermoplastic material is prepared by compounding athermoplastic polyether-amide block copolymer available from Atofina(France) under the trade name Pebax MV 3000 in the molten state with thepre-mix and with Irganox B 225 (anti oxidant agent) available fromCiba-Geigy. The liquid absorbing thermoplastic material has thefollowing composition: 24% Pebax MV 3000 30% PEG 400 45% Aqualic L74  1%Irganox B 225

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this written document conflicts with any meaningor definition of the term in a document incorporated by reference, themeaning or definition assigned to the term in this written documentshall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A process for making a liquid absorbing thermoplastic materialcomprising a matrix of a thermoplastic polymeric composition andparticles of an absorbent material dispersed in said matrix, whereinsaid thermoplastic polymeric composition comprises at least twocomponents, said process comprising the following steps: providing saidparticles of absorbent material; mixing said particles of absorbentmaterial with a first component in the liquid state of said at least twocomponents forming a pre-mix; and mixing said pre-mix with a secondcomponent of said thermoplastic polymeric composition in the moltenstate.
 2. The process according to claim 1, wherein said processcomprises the further step of grinding said particles of absorbentmaterial into said pre-mix to a selected average particle size.
 3. Theprocess according to claim 1, wherein said process comprises the furtherstep of grinding said particles of absorbent material into saidthermoplastic polymeric composition to a selected average particle size.4. The process according to claim 1, wherein said particles of absorbentmaterial include particles of water-insoluble water-swellable absorbentmaterial.
 5. The process according to claim 1, wherein said particles ofabsorbent material include particles of liquid gelling material.
 6. Theprocess according to claim 1, wherein said first component of saidthermoplastic polymeric composition in said pre-mix is liquid at roomtemperature.
 7. The process according to claim 6, wherein said firstcomponent has a viscosity at room temperature below about 30,000centipoise.
 8. The process according claim 1, wherein said particles ofabsorbent material have an average particle size below about 150μ. 9.The process according to claim 1, wherein said thermoplastic polymericcomposition comprises a thermoplastic polymer and a compatibleplasticiser.
 10. The process according to claim 9, wherein said firstcomponent in said pre-mix is said compatible plasticiser.
 11. Theprocess according to claim 9, wherein said thermoplastic polymer isselected from the group consisting of: polyurethanes, poly-ether-amidesblock copolymers, polyethylene-acrylic acid and polyethylene-methacrylicacid copolymers, polyethylene oxide and its copolymers, ethylene acrylicesters and ethylene methacrylic esters copolymers, poly lactide andcopolymers, polyamides, polyesters and copolyesters, polyester blockcopolymers, sulfonated polyesters, poly-ether-ester block copolymers,poly-ether-ester-amide block copolymers, polyacrylates, polyacrylicacids and derivatives, ionomers, polyethylene-vinyl acetate with a vinylacetate content of at least 28% by weight, polyvinyl alcohol and itscopolymers, polyvinyl ethers and their copolymers,poly-2-ethyl-oxazoline and derivatives, polyvinyl pyrrolidone and itscopolymers, thermoplastic cellulose derivatives, poly-caprolactone andcopolymers, poly glycolide, polyglycolic acid and copolymers, polylacticacid and copolymers, polyureas; and said compatible plasticiser isselected from the group consisting of citric acid esters, tartaric acidesters, glycerol and its esters, sucrose esters, adipates, sebacates,sorbitol, epoxidized vegetal oils, polymerised vegetal oils, polyols,phthalates, liquid polyesters, glycolates, glycols and polyglycols andtheir derivatives, sorbitan esters, phosphates, monocarboxylic fattyacids (C₈-C₂₂) and their derivatives, mineral oils, high boiling pointalcohols, glycerine, glycol ethers.
 12. The process according to claim1, wherein said pre-mix comprises from about 40% to about 80%, by weightof said pre-mix, of said particles of absorbent material, and from about20% to about 60%, by weight of said pre-mix, of said first component ofsaid thermoplastic polymeric composition.
 13. The process according toclaim 1, wherein said liquid absorbing thermoplastic material comprisesfrom about 10% to about 90% by weight of said liquid absorbingthermoplastic material, of said particles of absorbent material.